Portable electronic appliances such as cellular phones and smartphones are now growing in demand. Such electronic appliances each bear a compact and thin imaging unit. The imaging unit generally includes optical components such as a solid-state image sensing device (such as a CCD image sensor or CMOS image sensor) and lenses. Two or more lenses are used for higher resolution, and a light-shielding film is provided between the lenses so as to prevent ghosts and flares caused by undesired light from outside.
Patent Literature (PTL) 1 describes a light-shielding sealing agent that includes a light-shielding material; a curable resin having an unsaturated double bond, such as an epoxy (meth)acrylate or urethane (meth)acrylate; a polymerization initiator; and a thermal curing agent. Disadvantageously, however, the light-shielding material contained in the light-shielding sealing agent impedes ultraviolet irradiation to the inside of the curable resin. The sealing agent, upon curing by ultraviolet irradiation alone, is therefore cured at a low curing rate (is cured slowly) and requires, for example, a long-time heat treatment in addition to the ultraviolet irradiation. Thus, the light-shielding sealing agent requires an excessively long time to be cured.
PTL 2 describes a light-shielding film obtained by curing a light-shielding coating material, where the coating material includes a light-shielding material, an epoxy resin, and an amine curing agent. Unfortunately, however, the light-shielding coating material also fails to be cured rapidly by ultraviolet irradiation and requires an excessively long time to be cured, as with the technology described in PTL 1. Specifically, the light-shielding coating material requires an additional curing process typically of drying at room temperature for 60 minutes and further heating at 80° C. for 120 minutes. In addition, the light-shielding film is affixed to the lenses via an adhesive layer. The resulting assembly of components is, however, demanded to be thinned associated with size reduction and performance improvement of imaging units.
In addition, imaging units to be mounted in portable electronic appliances require reflow heat resistance for efficient mounting.